Electronic storage tube

ABSTRACT

An electronic storage tube having a target which is composed of an insulating layer having an electrode on each surface thereof. One of the electrodes is overlaid on one of the surfaces of the insulating layer in a pattern of stripes or cross-stripes and the exposed areas of the insulating layer are scanned by electron beams to establish a storage charge pattern. Different potentials are applied to the two electrodes to cause them to operate in a wide dynamic range.

United States Patent [191 Sato et al. Nov. 11, 1975 [5 ELECTRONICSTORAGE TUBE 3.670.198 6/!972 Lehovec 315/11 3.675.134 7/1972 Luedicke313/394 Inventors: Hiroki Sato, Yokohama;

Toseki Saito, Matsudo; Koji Hirano, Yokohama; Hiroh Takahashi,

Sony Corporation, Tokyo, Japan Foreign Application Priority Data Dec. 8.i972 Japan US. Cl 315/12; 3l3/394 Int. Cl. i. H01] 29/41 Field of SearchReferences Cited UNITED STATES PATENTS 8/l968 Shoulders PrimaryEmminer-Maynard R. Wilbur Assistant Examiner-J. M. Potenza Attorney.Agent, or FirmLewis H. Eslinger. Esq.; Alvin Sinderbrand ABSTRACT Anelectronic storage tube having a target which is composed of aninsulating layer having an electrode on each surface thereof. One of theelectrodes is overlaid on one of the surfaces of the insulating layer ina pattern of stripes or cross-stripes and the exposed areas of theinsulating layer are scanned by electron beams to establish a storagecharge pattern. Different potentials are applied to the two electrodesto cause them to operate in a wide dynamic range.

15 Claims, 12 Drawing Figures ELECTRONIC STORAGE TUBE BACKGROUND OF THEINVENTION l. Field of the Invention The present invention relates mainlyto an electronic storage tube and more particularly to the operation ofa grid control type of storage tube using a storage target of insulatingmaterial which has electrodes on both surfaces thereof.

2. Description of the Prior Art A conventional electron image storagedevice such as that disclosed in U.S. Pat. No. 3,631,294 is providedwith a single storage target. In that tube an electron gun directs anelectron beam at a target on the inner face of the tube. The targetconsists of an electrode layer of silicon with an insulating layercovering the surface of the electrode layer that faces the gun. Theinsulating layer has apertures in it through which electrons from thegun can reach the electrode.

The tube has four modes for each operating cycle: ready, writing, readout," and erase." In the ready mode, a relatively low voltage of about20 volts is applied to the target and the potential on the side of theinsulator facing the electron source is zero volts. To record a patternof information over the surface of the target, the target voltage israised to the write" level of, for example, 200 volts. At this level,the secondary emission ratio of the apertured insulator layer is greaterthan unity, the voltage at the surface of the insulating layer facingthe electron source will be 180 volts, which is the target voltage of200 volts less the voltage difference of 20 volts that was presentbetween the two surfaces of the insulator during the ready" mode.Information is then stored, or written, by scanning the target surfacewith a beam of electrons from the electron source.

In the read out" mode, the target voltage is reduced to, for example, 5volts. Then, when the electron beam scans the target, some of itselectrons will be repelled according to the stored charge pattern.

In the erase mode, the target voltage is again raised, for example to200 volts, and the beam is caused to scan the surface again.

The reason why the erase process is thus necessary is that if the erase"process were omitted and the "read out" process were directly followedby the ready" process, the scanning carried out by a beam of low levelof energy such as would be the case for a target voltage of volts duringthe ready" process, as mentioned above would require a long time tobalance the surface potential V to zero volts across its entire surface.Accordingly, the written signal must be erased by such an erase process.

In the storage tube of the above construction, the larger the aperturearea of the insulator layer, which is the same thing as saying that thelarger the area of catching beams on the target electrode is, the largerthe output of the tube is. On the other hand, if the aperture area ismade large, the surface potential required to cut-off the beam at theread out" time must have a large negative value. As a result, themaximum voltage across the insulating layer at the write" time isrequired to increase. This means that the voltage across the insulatinglayer at the ready" process must be made large. However, this voltagemust also be made less than the withstanding voltage of the insulatinglayer, which is the maximum permissible voltage that can be appliedacross it.

It is an object of this invention to provide an improved storage targetfor an electronic storage tube so as to produce a large output signalvIt is another object of this invention to provide a method of storing animage on a target ofan electronic storage tube so as to have a highsignal-to-noise ratio.

It is a further object of this invention to provide a method of storingan image on a target of an electronic storage tube in which theprocesses of one cycle from write" to "ready" for the next writing aresimplified.

It is a still further object of this invention to provide a method ofstoring an image on a target of an elec tronic storage tube in which thetime from a read out" condition to the completion of a "ready conditionfor the next writing is shortened.

Further objects will be apparent from the following specification anddrawings.

SUMMARY OF THE INVENTION In the present invention, separate electrodesare provided on both major surfaces of a storage insulator to form atarget. A voltage across the thickness of the insulator can be freelyestablished for the simultaneous enforcement of erase" and ready"processes. Further, the potential range of storage areas on the surfaceof the insulator can be selected to be large, since a voltage appliedthereto can be established in both polarities.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic cross-sectionalview showing a conventional electronic storage tube;

FIG. 2 is an enlarged cross sectional view showing a target of thestorage tube of FIG. 1;

FIG. 3 is a graph showing the relation between secondary emission ratioof an insulator layer and target voltage which is used for itsexplanation;

FIG. 4 is a schematic cross-sectional view showing one example of astorage tube according to this invention;

FIG. 5 is an enlarged cross-sectional view showing the principal part ofthe target according to this invention;

FIG. 6 is a view showing the equivalent circuit of the target accordingto this invention;

FIG. 7 is an enlarged cross-sectional view of the principal part showinganother example of the target according to this invention; and

FIGS. 8A-8E are process views showing one example of the method forfabricating the target according to this invention.

DETAILED DESCRIPTION OF THE INVENTION In the tube in FIG. 1 whichcorresponds to that in U.S. Pat. No. 3,63l,294, an electron beamemitting source, or an electron gun G is composed ofa cathode K, a firstgrid G a second grid G and a third G A voltage of, for example, volts tozero volts is applied to the first grid G, in accordance with writingsignals while constant voltages of 300 and 450 volts are applied to thesecond and thirds grids G and 6;, respectively. Reference numerals 2 and3 indicate an alignment coil and a deflection coil, respectively. Atarget 4 is disposed on a face plate la of the tube envelope l and abeam landing adjusting grid G located opposite the target 4.

As shown in FIG. 2, the target 4 comprises an electrode 5 on the innersurface of the face plate la of the envelope 1 and made of, for example,a silicon (Si) layer 5 and an insulator layer 6 made of silicon dioxide(SiO which is formed by oxidizing the surface of the electrode 5. Theinsulator layer 6 has a plurality of apertures 7 formed byphoto-engraving so that the electrode 5 is partially exposedtherethrough at its surface.

A storage tube of such construction is operated by the repetition offour processes, that is, ready, write, read-out and erase.

A description will first be given of the ready" process. In the readyprocess, a target voltage V applied to the electrode 5 is selected tobe, for example, volts with respect to the cathode K. The secondaryelectron emission ratio 8 of the insulator layer 6 is made 5 l and isvaried according to the energy of electron beam bombarding it. Thisenergy corresponds to the target voltage V as shown in FIG. 3. In thecase of the SiO layer 6, the ratio 8 has values such as 1 when thevoltage V is less than 40 volts and 8 l when the voltage V is more than40 volts. When the voltage V 20 volts, making 8 l as described above,the target 4 is scanned by an electron beam 8 emitted from the electrongun G. If the scanning is repeated, 2 potential V on the surface of theinsulator layer facing the cathode K is balanced with the cathodepotential at zero volts. As a result there will be a voltage E V, Vbetween the opposite surfaces of the insulator layer 6. The voltage E,can be selected to have a large value by selecting the voltage value ofV to be large, but in the practical case this value is selected to beless than the withstanding voltage of the insulator 6, for example about20 volts.

At the next stage the write" operation according to the aimed signal iscarried out. To carry out the writing, the potential V applied to theelectrode 5 is first selected to have a value to make the ratio 8 of theinsulator layer 6 8 l for example, 200 volts. lfthe potential V, is thusselected to be 200 volts, the surface potential V of the insulator layer6 will be such as V V-, E 200 20 180 volts. When the electron beam 8 issubjected to density modulation in accordance with the writing signalunder this condition, since the insulator layer 6 is in a conditionshowing 5 l, the surface potential V of the insulator layer 6 becomesmore positive in response to beam density and finally increases to 200volts. That is, the voltage V can be varied in a range of 180 to 200volts according to the writing signal. Thus, the distribution ofpotentials according to the writing signals forms a pattern ofpotentials on the surface of the insulator layer 6. In this case,theoretically writing can be effected with the voltage V in a rangebetween 180 and 200 volts, that is, within a range of 20 volts, butpractically the voltage V, is varied in a l5 volt range between 180 andI95 volts to maintain a linear characteristic, In other words, thewriting is carried out as a potential pattern in which the voltage Eapplied to the insulator layer 6 typically E; V V 200 (ISO to 195), orbetween about 20 volts and 5 volts.

Next, this written pattern is read out as follows. At first, the targetV is lowered to, for example, 5 volts. As a result, the surfacepotential V is changed with a distribution in accordance with thewritten pattern.

That is, since the written pattern is formed by the distribution ofE,,,-, which is in the range from 5 to 20 volts, the surface potential Vis distributed as a potential pattern in a range of V,,= V E =5 (5 to20)=0 to l 5 volts. When the scanning is carried out by the electronbeam 8 with the above condition, the beam moving through the aperture 7of the insulator layer 6 to the target electrode 5 is modulatedaccording to the distribution of the surface potential V of theinsulator layer 6 so that it is restrained from reaching the electrode 5at an area where the surface potential V has a large negative value toreduce a target current. That is, an output is obtained in accordancewith the written pattern.

After the completion of the read out process, the written pattern iserased. In order to carry out the erase" operation, the target voltage Vis changed to a value at which the ratio of the insulator layer 6 can be8 l, for example, 200 volts, and beam scanning is effected. Thus, thesurface potential V is balanced with 200 volts which is the same as Vand hence the voltage E becomes zero.

A description will now be given on one example of an electronic storagetube according to the present invention with reference to FIGS. 4 and 5.Elements of FIGS. 4 and 5 corresponding to those of FIGS. 1 and 2 areindicated by the same reference characters and without repeating theirdescription.

In the present invention, a target 13 includes a target electrode 9deposited on the inner surface of an insulating base plate or the faceplate la of the tube envelope 1, an insulator layer 10 formed over theface plate la, and a signal electrode 12 formed on the layer 10 andhaving a plurality of small boxes or slit-like apertures 11 throughwhich the insulator layer 10 is partially exposed. Thus, a capacitiveelement C is equivalently formed at each aperture 11 so that theelectrode 12 is disposed adjacent to each capacitive element.

The target electrode 9 can be formed by vaporization of, for example, alayer of chromium Cr with a thickness of about 3,000 A. The insulatorlayer 10 is formed in such a manner that the surface of the electrode 9made of chromium is oxidized to a thickness of about several tens of Ato form chrome oxide (CrO) as its foundation. A layer of SiO or SiOhaving a thickness of about I to 5 microns (u) is vaporized on the CiOlayer. Further, the signal electrode 12 is formed by vaporization of,for example, a layer of aluminum (Al) having a thickness of about 1,000to 2,000 all over the surface. The apertures II are formed byphotoengraving.

Operation of the storage tube according to this invention will now bedescribed. At first, a condition ready for writing is establised. Inthis condition the voltage V applied to the target electrode 9 isselected to be, for example, 200 volts, while the voltage V applied tothe signal electrode 12 is selected to be volts, or about 20 volts lessthan the voltage V With electrodes at these voltages, an electron beam14 is emitted from the electron beam emitting source or gun to scan thetar get. The secondary emission ratio 8 of the insulator layer 10 ishigh enough so that 6 l as described with reference to FIG. 3. As aresult, the surface of the capacitve element C exposed through theaperture 11 and bombarded by the electron beam discharged secondaryelectrons, causing the surface to be positively charged. However, itssurface potential V is balanced by 180 volts ofthe potential Vp of theelectrode 12. That is, the potential V, becomes equal to 180 volts. Thereason that the surface potential V, is balanced with the potential V isthat, when the insulator layer is bombarded at its surface by theelectron beam, the secondary electrons are discharged to enhance thepotential at that surface, causing the latter to become positive asdescribed previously. However, if the potential V becomes higher thanthe potential V the discharged electrons are repelled by the electrode12 having the potential V to be combined with positive charge on thesurface of the insulator layer 10, with the result that the surfacepotential V is not increased to a value higher than V but is finallybalanced with the potential V Accordingly, the voltage E applied to thecapacitive element C in the aperature 11 formed by the insulator layer10 becomes E V,- V 200 180 20 volts. The voltage E, can be freely chosenby the selection of the respective voltages V, and Vp of the electrodes9 and 12, but it is preferable that it be less than the withstandingvoltage of the insulator layer. Hence, the voltages V and V are selectedso as to make the voltage E for example, 20 volts. Further, the voltageV should have a low enough value that the electron beam may be providedwith enough energy to make the surface potential V equal to thepotential V quickly by a small number of scannings.

With these voltages applied to the tube 1, the writing in response tothe aimed signal is carried out. The voltage V applied to the signalelectrode 12 is raised to a value higher than V for example, to 220volts, and the voltage V applied to the electrode 9 is kept at, forexample, 200 volts. If the electron beam is subjected to densitymodulation in response to the writing signal under this condition inwhich the insulator layer 10 is in a condition such that 8 1, thesurface potential V in the aperture 11 of the insulator layer 10 will bevaried in a range from 180 volts, which was present during the readyprocess to the 220 volts applied to the electrode 12 at the presentstage. The potential V will be lSO volts at areas where no writing iscarried out by the electron beam but will be at the 220 volt maximumvalue at other areas where a great amount of electron beam is radiated.In this way, the surface potential V of the capacitive element C will beprovided with a potential pattern that has a potential distribution of180 to 220 volts as determined by the writing signal. Thus, in thisinvention, the surface potential V which varies according to writing,can have a range of 40 volts, i.e., from 180 to 220 volts. Even thoughits linear characteristic is taken into consideration, the surfacepotential V, is in a range of 35 volts, i.e., between 180 to 215 volts,which is substantially greater than the prior example that has a rangeof only about 15 volts, as described in FIGS. 1 and 2. However,attention must be paid to the fact that, although the writing range is35 volts as mentioned above, the voltage applied to the insulator layer10 is the difference between the voltage V which is 200 volts, and thevoltage V which may be 220 volts, making the difference approximatelyequal to volts between the opposite electrodes 9 and 12. The voltageapplied to the capacitive element C or the voltage E across thethickness of the insulator layer 10 in the aperture 11 is E V V 200 (180to 215) 20 to l5 volts which means that the maximum voltage appliedthereto is only 20 volts, so that all of the voltages applied to therespective portions of the insulator layer [0 can be kept below theinsulation breakdown voltage.

Next, in order to read out the written pattern, the potential V of thetarget electrode 9 is selected to be, for example, 20 volts and thevoltage V applied to the signal electrode 12 is selected to be, forexample, [0 volts. Since, at this time, the potential difference Ii,-across the thickness of the capacitive element C is distributed in arange of 20 to l5 volts for writing, the surface potential V of eachelement C is distributed in a range of V E; 20 (20 to 15) 40 to 5 voltsor in a range of 35 volts. When the scanning is ef fected by theelectron beam 14 under this condition, the electron beam 14 is modulatedin accordance with the surface potential V, of each capacitive element Cso that the electron beam may not easily reach the electrode 12particularly adjacent to a portion of the element C where the surfacepotential V; thereofhas large negative value. Thus, the beam current ismodulated according to the written pattern, so that a signal output inresponse to the written pattern is derived from the signal electrode 12.

After the read out" process, the written pattern is erased. This erasingoperation can be carried out simultaneously with the ready" processdescribed above. That is, a voltage of 200 volts, for example, isapplied to the target electrode 9 to make the secondary emission ratioofthe insulator layer 10 5 l and to provide a high level of energy tothe electron beam so that the surface potential V of the capacitiveelement C can be quickly balanced with the potential V of the signalelectrode 12. A voltage of I volts is applied to the signal electrode 12to establish a predetermined potenial difference for example, 20 voltsbetween the opposite ends of the capacitive element C.

After the write and read out operations are thus completed, the readycondition for the following writing can be rapidly established.

In the construction described above, the insulator layer 10 isrequiredto prevent the production of pinholes or the like, which might connectthe electrodes 9 and 12. For this purpose it is desirable to make theinsulator layer 10 as thick as possible. On the other hand, it ispreferable for the insulator layer 10 to be thin to make the capacitanceof the element C large. In the target of the storage tube according tothis invention the equivalent circuit of which is shown in FIG. 6, astray capacity C, is formed between each capacitive element C and signalelectrode 12. The surface potential V of the element C and the potentialV of the electrode 12 are made equal in the "erase and ready" process,but in the write process they are made different and hence a potentialdifference V is provided there between. Thus, the surface potential V isvaried by the influence from the voltage applied to the signal electrodel2 and its variation AV is given as Accordingly, in order to make thevariation as small as possible, it is necessary to make C, small and Clarge. For this reason, the insulator layer 10 forming the capacitiveelement C should preferably be thin as men tioned above.

In order to increase the capacity of the capacitive element C and toensure the insulation between the electrodes 9 and ll, the insulatorlayer is constructed with thin patrons [0A thickness 1, which forms thecapacitive elements C and thick portions 108 of thickness 1 which formsthe electrodes 12 as shown in FIG. 7. The insulator layer havingportions 10A and 10B of different thickness I and r is constructed bymaking the insulator layer 10 so that its original thickness isrelatively great. Sections of this thick layer 10 are partially etchedaway a required depth to form the portion 10A with a thickness r,.However, it is difficult to stop the etching at the required depth forthe insulator layer 10 and to perform the etching with no side-etchingbeing caused for the thick insulator layer. In this case, a specialmethod is used in order to form the insulator layer 10 having a smallthickness t, at one part and a large thickness at the other part. Oneexample of this special method will now be described with reference toFIG. 8.

The target electrode 9 is formed by vaporization of, for example,chromium entirely on the substrate or face plate In. Then, on theelectrode 9 there are successively deposited more than two layer, forexample, first, second and third insulating layers 10a, lOb and [0c byutilizing a well known technique such as a thermal cracking method orthe like (FIG. 8A). The first insulating layer 10a is formed of amaterial providing a large value of the secondary emission ratio 6 bythe bombardment of electrons having a proper level of energy. Forexample. the layer 100 may be MgF CaF or the like deposited on the faceplate la with the thickness 1,, for example, 5,000A suitable forconstructing the capacitive element C as described in connection withFIG. 7. The second insulating layer 10b is formed by depositing on thelayer 100 a material which is capa ble of being etched differently fromthe first insulating layer 100 and provides almost no corrosion to thefirst insulating layer 10a by its etching liquid, for example, M 0 Thethickness of the second layer 10b may be, for example, 5,000A. Further,the third insulating layer 10c, made ofsuch a material different fromthose of the first and second insulating layers 10a and 10b but capableof being etched is formed by deposition on the layer 10b. The layer 10cmay be SiO having a thickness of about I The material of this layer isalso not corroded substantially by the etching liquids for the first andsecond insulating layers. The total thickness of the first, second andthird insulating layers 10a, 10b and 10c is equal to the large thicknessr required between the both electrodes 9 and 12 as described inconnection with FIG. 7.

On the third insulating layer 10c, there is deposited a metal layer 12which finally forms the electrode 12 (FIG. 8B). The metal layer 12' canbe formed by vaporization, of, for example, a gold layer on a chromiumlayer.

On the metal layer 12' exepting portions where the apertures ll of theelectrode 12 are formed therethrough, there is deposited by opticalprocessing a photo resist 15 that serves as an etching resist to themetal layer 12' (FIG. 8C).

The metal layer 12' is etched, except where covered by the resist 15, toremove unnecessary portions and thereby form the electrode 12 (FIG. 8D).

Next, with this electrode 12 being used as a mask, the third insulatinglayer 106 made of, for example, SiO is etched by fluoric acid to form anaperture 16 inside the aperture 11. Further, with this third insulatinglayer 10c being used as a mask, the second insulating layer 10b isetched through the aperture 16 by an etching liquid, for example, heatedphosphoric acid to provide an aperture l7 coincident with the aperture16(FIG.8E). At this time, the first insulating layer 10a is not corrodedby the etching liquid for the second insulating layer 10b, so that thelayer 10:: remains as it is.

According to the above described method, between the opposite electrodes9 and 12 the respective insulating layers 10a, lOb and 100 remain asthey are to form the insulator layer 10 with the large thickness 1 equalto the sum of those of the respective layers, so that the insulationbetween the electrodes 9 and 12 can be positively maintained. At areasforming the capacitive ele ment C inside the aperture 11 of theelectrode 12, the insulator layer 10 is formed with the small thicknessr, equal to that of the single insulating layer 10a by a recess 18formed with the apertures 16 and 17, so that the capacity of thecapacitive element C can be made large.

However, the portion between the electrodes 9 and 12 is formed not bythe single insulating layer with large thickness but by a pluralityofdifferent insulating layers being overlapped successively and hencethere is little possibility that the pinholes or defective portions inthe layers 10a, 10b and I00 will be coincident with one another so as toconnect the electrodes 9 and 12 and cause a troublesome short-circuitbetween the electrodes 9 and 12.

When the above described method is used, the insulator layer 10 isformed by overlapping the insulating layers 10a, lOb and 10c thatrespond to different etching liquids. Accordingly, even though a deeprecess 18 is formed inside the aperture 11 of the insulator layer 10, itis possible to prevent the recess 18 from being enlarged byside-etching. In addition, since the thickness 1, of the portion formingthe capacitive element C is defined by the thickness of the insulatinglayer 100, in the case of forming the recess 18 high accuracy in controlof the etching process is not necessary for the control of its depth.Thus, the uniformity of productivity and characteristics of the targetscan be improved.

The method for concretely forming the target 13 and its construction arenot limited to the above-mentioned example. The face plate of the tubeenvelope is used as the base plate in the foregoing example, but it isalso possible for electrodes to be vaporized on opposite surfaces of abase plate, for example, a glass plate about 40y. thick. Thereafter theexposed surface of the signal electrode side is etched about 1 to 2p. toform a target which is attached to the face plate.

According to this invention, separated from the target electrode 9 thereis also provided the signal electrode 12 to which the potential Vdifferent from the target potential V if applied. This has severaladvantages. For example, the erase" and ready processes can be carriedout at the same time, though they may be effected separately. In otherwords, the potential V, of, for example, 200 volts is applied to theelectrode 9 while a potential V of l volts is applied to the electrode12. With such an arrangement, an electron beam having a large level ofbombarding energy is emitted to erase the previously written informationquickly and to complete the ready condition in which the voltage E, ofabout 20 volts is applied to the capacitive element C. Accordingly, thedrive and circuit arrangement to be used with the tube of this inventioncan be simplified and also the time period from "read out" to thebeginning of following writing can be shortened.

Further, when the writing is carried out, the potential V, of theelectrode 12 can be raised to a value different from that of theelectrode 9, for example, 220 volts. Thus, the writing can be made onthe capacitive element C in a range between positive and negativevoltages with the potential of the electrode 9 as the referencetherebetween, so that a voltage range more than twice that of theconventional storage tube can be theoretically provided. The writing canbe effected in a range of better linearity and also in the case of "readout" process the information can be derived as a large output, so thatthe signal-to-noise ratio can be enhanced. In addition, irrespective ofthe large output, the voltage applied to the insulator layer can be madelower than its insulation break-down voltage at the respective portions.

Further, the storage tube according to this invention is not limited tothe storage of electric charge but can be used as a light-electricitytransducer, that is, as an image pickup tube. In the latter case, atarget electrode is formed by a transparent conductive layer such asNESA, while a storage insulating layer is formed by a photoconductivelayer such a three-element compound of As-Sb-S on which a signalelectrode of mesh type or stripe-type is formed. Thus a target isprovided. In the "ready" process, a voltage of, for example, 30 volts isapplied to the target electrode while the signal electrode is energizedwith, for example, zero volts. The target is then scanned by an electronbeam. In the write process, an optical pattern is projected from theside of transparent electrode. The amount of light causes thephotoconductive layer to change its resistance, thereby changing itssurface potential. The surface potential approaches 30 volts at areaswhere no light is projected. On the other hand, in the "read out"process, the target electrode is energized by a voltage of, for example,zero volts while the signal electrode is energized by a voltage of, forexample, 5 volts. When the scanning is carried out by an electron beamunder the latter condition, a current according to the optical patterncan be derived from the signal electrode. This system is not of a typein which the charging and discharging currents of a capacitance in thephotoconductive layer are read out as in the case of vidicon. Thissystem is of a grid control type, so that the read out operation can berepeatedly carried out.

What is claimed is:

1. A storage tube comprising:

A. a target comprising:

1. a first conductive layer,

2. an insulating layer thereon, and

3. a second conductive layer, said second conductive layer comprising apattern of apertures through which said insulating layer is directly exposed; the insulating layer being thinner at regions corresponding toeach of said apertures than at regions covered by solid portions of saidsecond conductive layer;

B. an electron source to direct electrons at said second conductivelayer and the exposed portions of said insulator layer; and

C. means to apply different potentials to said first and secondconductive layers to establish, selectively, conditions for recording acharge pattern of electrons from said source on said insulating layerand for reading said pattern and for erasing said pattern.

2. The storage tube of claim 1 in which said insulating layer comprisesa plurality of layers of insulating material responsive to differentetching materials whereby selected areas of said insulating layer may beetched to controlled depths.

3. A method of storing an image in a storage tube comprising electronemitting means and a target including a storage material having firstand second surfaces, a first electrode provided on said first surface ofthe storage material, and a second electrode partially provided on saidsecond surface of the storage material, said second surface having astorage area to be scanned by an electron beam from said electronemitting means, said method comprising the steps of: applying first andsecond potentials to said first and second electrodes, respectively, thefirst and second potentials having a value sufficient to cause secondaryelectron emission from said storage area when scanned by said electronbeam but the potential difference therebetween being less than thebreakdown voltage of said storage material, to make said storage areasubstantially the same potential; applying third and fourth differentpotentials to said first and second electrodes, respectively, toestablish a charge pattern on said storage area; and applying fifth andsixth potentials to said first and second electrodes, respectively, todetect said pattern.

4. A method of storing an image on a target according to claim 3 whereina reference potential is applied to said electron emitting means.

5. A method of storing an image on a target according to claim 3 whereinsaid first potential is higher than said second potential to provide apotential difference between said surfaces of the material.

6. A method of storing an image on a target according to claim 4 whereinsaid third and fourth potentials are sufficiently higher than saidreference potential to cause secondary electron emission from saidstorage area.

7. A method of storing an image on a target according to claim 6 whereinsaid fourth potential is higher than said third potential.

8. A method of storing an image on a target according to claim 4 whereinsaid fifth potential is lower than said reference potential.

9. A method of storing an image on a target according to claim 8 whereinsaid sixth potential is higher than said reference potential.

10. A method of storing an image on a target according to claim 3wherein said storage material is a photoconductive material and saidfirst electrode is transparent.

ll. A method of storing an image on a target according to claim 10wherein said charge pattern depends on incident light.

12. A method of storing an image in a storage tube comprising electronemitting means and a target including a storage material having firstand second surfaces, a first electrode provided on said first surface ofthe storage material, and a second electrode partially provided on saidsecond surface of the storage material, said second surface having astorage area to be scanned by an electron beam from said electronemitting means, said method comprising the steps of: applying first andsecond potentials to said first and second electrodes, respectively, thefirst potential being greater than the second potential, to make saidstorage area substantially the same potential when scanned by saidelectron beam; applying third and fourth potentials to said first andsecond electrodes, respectively, the fourth potential being greater thanthe third potential and being of sufficient value to cause secondaryemission from said storage area when scanned by said electron beam so asto establish a charge pattern on said storage area; and applying fifthand sixth potentials to said first and second electrodes, respectively,to detect said pattern.

13. A method of storing an image in a storage tube in accordance withclaim 12 wherein said established charge pattern has a potentialdistribution within a range defined by the difference between saidsecond and fourth potentials.

14. A method of storing an image in a storage tube comprising electronemitting means and a target including a storage material having firstand second surfaces, a first electrode provided on said first surface ofthe storage material, and a second electrode partially provided on saidsecond surface of the storage material, said second surface having astorage area to be scanned by an electron beam from said electronemitting means, said method comprising the steps of: applying first andsecond different voltage potentials to said first and second electrodes,respectively, to make said storage area substantially the same potentialwhen scanned by said electron beam; applying third and fourth differentpotentials to said first and second electrodes, respectively, so as toestablish a charge pattern on said storage area, and applying fifth andsixth different potentials to said first and second electrodes,respectively, the difference between said fifth and sixth potentialsbeing at least as great as the range of the potential distributioncorresponding to said charge pattern on said storage area.

15. A method of storing an image in a storage tube comprising electronemitting means and a target including a storage material having firstand second surfaces, a first electrode provided on said first surface ofthe storage material, and a second electrode partially provided on saidsecond surface of the storage material, said second surface having astorage area to be scanned by an electron beam from said electronemitting means, said method comprising the steps of: applying first andsecond potentials to said first and second electrodes, respectively, thefirst potential being greater than the second potential and having avalue sufficient to cause secondary electron emission from said storagearea when scanned by said electron beam, but the difference between saidfirst and second potentials being less than the breakdown voltage ofsaid storage material, to make said storage area substantially the samepotential; applying third and fourth potentials to said first and secondelectrodes, respectively, the fourth potential being greater than thethird potential and being of sufficient value to cause secondaryemission from said storage area when scanned by said electron beam so asto establish a charge pattern on said storage area having a potentialdistribution within a range defined by the difference between saidsecond and fourth potentials; and applying fifth and sixth potentials tosaid first and second electrodes, respectively, the difference betweensaid fifth and sixth potentials being at least as great as said range ofpotential distribution on said storage area.

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1. A storage tube comprising: A. a target comprising:
 1. a firstconductive layer,
 2. an insulating layer thereon, and
 3. a secondconductive layer, said second conductive layer comprising a pattern ofapertures through which said insulating layer is directly exposed; theinsulating layer being thinner at regions corresponding to each of saidapertures than at regions covered by solid portions of said secondconductive layer; B. an electron source to direct electrons at saidsecond conductive layer and the exposed portions of said insulatorlayer; and C. means to apply different potentials to said first andsecond conductive layers to establish, selectively, conditions forrecording a charge pattern of electrons from said source on saidinsulating layer and for reading said pattern and for erasing saidpattern.
 2. an insulating layer thereon, and
 2. The storage tube ofclaim 1 in which said insulating layer comprises a plurality of layersof insulating material responsive to different etching materials wherebyselected areas of said insulating layer may be etched to controlleddepths.
 3. A method of storing an image in a storage tube comprisingelectron emitting means and a target including a storage material havingfirst and second surfaces, a first electrode provided on said firstsurface of the storage material, and a second electrode partiallyprovided on said second surface of the storage material, said secondsurface having a storage area to be scanned by an electron beam fromsaid electron emitting means, said method coMprising the steps of:applying first and second potentials to said first and secondelectrodes, respectively, the first and second potentials having a valuesufficient to cause secondary electron emission from said storage areawhen scanned by said electron beam but the potential differencetherebetween being less than the breakdown voltage of said storagematerial, to make said storage area substantially the same potential;applying third and fourth different potentials to said first and secondelectrodes, respectively, to establish a charge pattern on said storagearea; and applying fifth and sixth potentials to said first and secondelectrodes, respectively, to detect said pattern.
 3. a second conductivelayer, said second conductive layer comprising a pattern of aperturesthrough which said insulating layer is directly exposed; the insulatinglayer being thinner at regions corresponding to each of said aperturesthan at regions covered by solid portions of said second conductivelayer; B. an electron source to direct electrons at said secondconductive layer and the exposed portions of said insulator layer; andC. means to apply different potentials to said first and secondconductive layers to establish, selectively, conditions for recording acharge pattern of electrons from said source on said insulating layerand for reading said pattern and for erasing said pattern.
 4. A methodof storing an image on a target according to claim 3 wherein a referencepotential is applied to said electron emitting means.
 5. A method ofstoring an image on a target according to claim 3 wherein said firstpotential is higher than said second potential to provide a potentialdifference between said surfaces of the material.
 6. A method of storingan image on a target according to claim 4 wherein said third and fourthpotentials are sufficiently higher than said reference potential tocause secondary electron emission from said storage area.
 7. A method ofstoring an image on a target according to claim 6 wherein said fourthpotential is higher than said third potential.
 8. A method of storing animage on a target according to claim 4 wherein said fifth potential islower than said reference potential.
 9. A method of storing an image ona target according to claim 8 wherein said sixth potential is higherthan said reference potential.
 10. A method of storing an image on atarget according to claim 3 wherein said storage material is aphotoconductive material and said first electrode is transparent.
 11. Amethod of storing an image on a target according to claim 10 whereinsaid charge pattern depends on incident light.
 12. A method of storingan image in a storage tube comprising electron emitting means and atarget including a storage material having first and second surfaces, afirst electrode provided on said first surface of the storage material,and a second electrode partially provided on said second surface of thestorage material, said second surface having a storage area to bescanned by an electron beam from said electron emitting means, saidmethod comprising the steps of: applying first and second potentials tosaid first and second electrodes, respectively, the first potentialbeing greater than the second potential, to make said storage areasubstantially the same potential when scanned by said electron beam;applying third and fourth potentials to said first and secondelectrodes, respectively, the fourth potential being greater than thethird potential and being of sufficient value to cause secondaryemission from said storage area when scanned by said electron beam so asto establish a charge pattern on said storage area; and applying fifthand sixth potentials to said first and second electrodes, respectively,to detect said pattern.
 13. A method of storing an image in a storagetube in accordance with claim 12 wherein said established charge patternhas a potential distribution within a range defined by the differencebetween said second and fourth potentials.
 14. A method of storing animage in a storage tube comprising electron emitting means and a targetincluding a storage material having first and second surfaces, a firstelectrode provided on said first surface of the storage material, and asecond electrode partially provided on said second surface of thestorage material, said second surface having a storage area to bescanned by an electron beam from said electron emitting means, saidmethod comprising the steps of: applying first and second differentvoltage potentials to said first and second electrodes, respectively, tomake said storage area substantially the same potential when scanned bysaid electron beam; applyIng third and fourth different potentials tosaid first and second electrodes, respectively, so as to establish acharge pattern on said storage area; and applying fifth and sixthdifferent potentials to said first and second electrodes, respectively,the difference between said fifth and sixth potentials being at least asgreat as the range of the potential distribution corresponding to saidcharge pattern on said storage area.
 15. A method of storing an image ina storage tube comprising electron emitting means and a target includinga storage material having first and second surfaces, a first electrodeprovided on said first surface of the storage material, and a secondelectrode partially provided on said second surface of the storagematerial, said second surface having a storage area to be scanned by anelectron beam from said electron emitting means, said method comprisingthe steps of: applying first and second potentials to said first andsecond electrodes, respectively, the first potential being greater thanthe second potential and having a value sufficient to cause secondaryelectron emission from said storage area when scanned by said electronbeam, but the difference between said first and second potentials beingless than the breakdown voltage of said storage material, to make saidstorage area substantially the same potential; applying third and fourthpotentials to said first and second electrodes, respectively, the fourthpotential being greater than the third potential and being of sufficientvalue to cause secondary emission from said storage area when scanned bysaid electron beam so as to establish a charge pattern on said storagearea having a potential distribution within a range defined by thedifference between said second and fourth potentials; and applying fifthand sixth potentials to said first and second electrodes, respectively,the difference between said fifth and sixth potentials being at least asgreat as said range of potential distribution on said storage area.